Abrasive belt grinding machine



y 1963 F. GEGAUF ABRASIVE BELT GRINDING MACHINE Filed Feb. 19, 1960 I INVEIVT'ORJ F/v/rz are/70F %w%%w United States Patent 3,095,675 ABRASIVE BELT GRINDING MACHINE Fritz Gegauf, Steckborn, Switzerland, assignor to Fritz Gegauf Aktiengesellschaft Bernina-Nahmaschinenfabrik, Steckborn, Switzerland Filed Feb. 19, 1960, Ser. No. 9,986 Claims priority, application Switzerland Feb. 19, 1959 1 Claim. (Cl. 51-148) This invention refers to a belt grinding machine for the grinding of work pieces the surfaces of which comprise curvatures having extremely small radii, grinding being effected in consecutive operation stages, without adjustment of the machine and without having to put down the work piece during the grinding operation.

In known abrasive belt grinding machines having an abrasive belt passing over a driving pulley and one or several rollers, an adjustable roller is provided to place the belt in operating position and to compensate for its length. This roller is fixed after having been adjusted. In most cases the driving pulley is formed as a contact grinding roller on which the grinding work is done in a similar way as with a normal grinding support having a circular grinding wheel. Frequently, grinding with such machines is effected between the rollers, the belt passing over a support or being applied by means of a pressure member against the work piece to be ground. However, when radii and curvatures are to be ground on a work piece, which difier in their dimensions, profiled driving pulleys are used as contact grinding wheels and must be exchanged for each particular shape to be ground. As in this working process the grinding pulley does not adapt itself to the surface of the work piece, the profiles are deformed through the grinding process, i.e. they are adapted to the profile of the grinding wheel. The grinding operations to be eliected on one work piece must be carried out in a plurality of operating steps resulting in long grinding periods and in a considerable loss of time, or by means of several grinding machines. For these reasons such known grinding methods are very expensive. When the grinding is done between the rollers, the curves which can be ground have to be quite flat, i.e., almost plane. It is altogether impossible to grind work pieces having curvatures of rdifierent radii in a single operation.

It is an object of the invention to eliminate these inconveniences by the provision of an abrasive belt grinding machine having an endless abrasive belt passing over a driving pulley and several guide rollers one of which is adjustable in its position, means being provided for changing the tension of the abrasive belt during operation, whereby the grinding of work pieces having surface curvatures of diiferent radii can be efiected in a continuous grinding operation.

The accompanying drawing illustratesby way of example a preferred embodiment of my invention. In the drawing:

FIGURE 1 represents a grinding machine in perspective view,

FIGURE 2 is a diagrammatic representation of the belt guiding and stretching equipment,

FIGURE 3 is a similar representation showing a work piece applied against the belt,

FIGURE 4 is a similar representation showing the grinding of a curved surface having a small radius of curvature.

With reference to FIGURE 1, the frame 1 of the grind machine carries a fixed supporting arm 2 for the belt guide rollers. An electric motor 3 is carried by the firame 1 or 2 and drives a smooth driving roller 4 journalled in the arm 2. The upper end of the arm 2 forms a bearing ice for a guide roller 5 and carries a movable arm 6 adapted to pivot about the axis of the roller 5. The outer end of the arm 6 forms a bearing for a further guide roller 7. An abrasive belt 8 passes over the three rollers 4, 5 and 7. A counter weight 9 acts as belt tensioner to compensate the varying length of the belt. The counter weight is slidably mounted on a rod 10 secured to the arm 6, and is fixed in its position by means of a screw 11. In order to adapt the tension of the abrasive belt 8 during the operation of the machine to the workpiece and to the particular kind of grinding work, a pull rod 12 has its lower end connected to a pedal 14 pivoted to the foot plank 13 of the machine frame, and its upper branched end attached to the counter weight 9. By means of pressure exerted on the pedal 14, the tension of the belt 8 can be adjusted according to the grinding work to be effected, in order to increase or decrease the pressure exerted on the workpiece and accordingly the grinding or chip removing action.

The operation of the described machine is as follows:

In FIGURES 3 or 4, the workpiece :15 or 16, respectively, is applied from below against the abrasive belt 8 with such a pressure that the flexible belt adapts itself to the contour of the portion of the workpiece to be ground.

The pivotable arm 6 then swings about its axis while lifting the counterweight 9, so 'far as is necessary for compensating the length of the belt 8. The grinding operation, i.e. the removal of chips, accordingly is effected under a resilient pressure. Exactly as in a hand operated grinding device where the abrasive belt is applied with more or less pressure against the workpiece, it is possible, in the described machine, to increase the pressure of the belt 8 on the workpiece by an increased action on the counterweight 9 by the pedal 14. By varying the pressure exerted upon the pedal, the tension of the belt 8 can be more or less increased. The workpiece 15- or 16 can be applied against the abrasive belt 8 with its difierent surface portions during running of the machine without requiring any change in setting.

Obviously, the described grinding machine is provided with the usual protection and suction devices. Only the portion of the belt 8 remains exposed on which the grinding operation is eliected and which is situated in the operators field of vision.

The described machine can undergo various modifications within the scope of the appended claim. For example the counterweight 9 can be replaced by springs the pressure of which can be changed by means of transmission levers operatively connected with the pedal 14. The pedal can be replaced by a lever for the adjustment of the tension of the abrasive belt.

I claim:

A grinding machine comp-rising a raised pedestal, a rigid bearing arm on said pedestal including a first bearing opening directly above said pedestal, said arm having an extension extending laterally and upwardly from said pedestal and having a second bearing opening therein, a driving motor mounted on said pedestal and having a shaft extending through said first bearing opening and terminating in a first guide roller, a tensioning arm member having a mounting shaft portion connected thereto extending through said second bearing opening and terminating in a second guide roller said tensioning arm with said shaft being rotatable in said second bearing, said tensioning arm having at its free end an outwardly extending shaft portion constituting a third guide roller aligned in a plane with said first and second guide rollers, an endless abrasive belt trained to run around each of said guide rollers, a weighted arm member connected to said tensioning arm and biasing said tensioning arm in a di- 3 4 reetion toward engagement with said abrasive belt and References Cited in the file of this patent away from said first guide roller for tensioning said belt, UNITED STATES PATENTS and pedestal means connected to said weighted member and movable to deflect said weighted arm member to ro- 258,076 Kahl May 161 1882 tate said tensioning arm member to increase the tension 5 782245 Hermann 141 1905 on Said abrasive belt 2,433,427 Carlsson Dec. 30, 1947 

